PROJECT ABSTRACT Pulmonary arterial hypertension (PAH) is a cardiovascular disease characterized by vascular proliferation and remodeling of the small pulmonary arteries, a progressive increase in pulmonary vascular resistance and right heart failure. Despite current therapies that target specific pathways in PAH pathogenesis- including prostacyclin derivatives, endothelin-receptor antagonists, and phosphodiesterase type 5 inhibitors- PAH- related morbidity and mortality remains high, indicating the need for novel therapeutic approaches. The goal of the proposed research is to evaluate the enhanced efficacy of combination gene therapy AAV1.SERCA2a with AAV1.BMPR2 on the remodeling of pulmonary artery smooth muscle cells (PASMC) and pulmonary artery endothelial cells (PAEC) dysfunction in PAH disease in vitro and in vivo. Our preliminary studies have demonstrated that SERCA2a expression decreases in parallel to decreases in BMPR2 in: 1) Small hypertrophied pulmonary arterioles from PAH patients (with and without BMPRII mutations), 2) A monocrotaline (MCT) rat model of PAH, and 3) SMC-specific transgenic mouse expressing a dominant- negative BMPRII under the control of the tetracycline gene switch (SM22-tet-BMPRIIdelx4 mice), known to develop spontaneous PAH. Based upon these preliminary findings we hypothesize that SERCA2a and BMPRII may mutually affect pulmonary vascular remodeling and that SERCA2a and BMPR2 combination gene transfer may reverse vascular remodeling and therefore PAH phenotype. We will test this hypothesis by: 1) Assessing the effects of the combined expression of SERCA2a and BMPR2 in vascular cells function in vitro, and 2) Evaluating the efficacy of intratracheal combination gene therapy of AAV1.SERCA2 and AAV1.BMPR2 on PAH pathogenesis in mouse model of PAH. There the combination gene therapy may lead to the identification of new potential targets for therapeutic intervention to overcome the pathological feature of PAH.